The present invention relates to a beam splitter which is provided in a color imaging equipment and separates incident beams into the three primary colors of red, green and blue.
FIGS. 1 and 2 are composition drawings showing a color imaging equipment with a prior beam splitter. FIG. 1 shows a plan view, and FIG. 2 shows an A--A' sectional side view of FIG. 1. In these figures, a taking lens 1, a beam splitter 2, and a solid-state image sensing device 3R, 3G and 3B are provided The beam splitter 2 provides a blue channel prism block 2B, a red channel prism block 2R, a green channel prism block 2G, and supporting plates 4. An air-gap 6 is formed between the blue channel prism block 2B and the red channel prism block 2R by means of a spacer 5. The red channel prism block 2R and the green channel prism block 2G are connected via a bonding layer 7. The supporting plates 4 are connected via bonding layers 8 to the prism blocks 2R, 2G and 2B, and by means of these supporting plates 4, the prism blocks 2R, 2G and 2B are mounted to a camera chassis (not shown). The solid-state image sensing devices 3R, 3G and 3B are mounted to the beam splitter 2 via spacers 10, respectively, so that they receive outgoing beams from the corresponding prism blocks 2R, 2G and 2B.
Beams received through the taking lens 1 are separated into color beams of red, green and blue by the beam splitter 2, and received by the solid-state image sensing devices 3R, 3G and 3B which are mounted to the respective color channels.
In the meantime, a characteristic which is of most importance in this type of color imaging equipment is a registration characteristic. The registration characteristic represents an amount of image deflection of the red channel Rch from the green channel Gch and of the blue channel Bch from the green channel Gch, with the green channel as the basis, as the number of television lines (TV lines). The registration characteristic required for a color imaging equipment is that the amount of image deflection from the green channel Gch is within 0.2 TV line for both the amount of image deflection Gch-Rch of the red channel Rch and the amount of image deflection Gch-Bch of the blue channel Bch, and these values must be assured within the working temperature range of -15.degree. C. through 60.degree. C.
FIG. 3 shows a temperature characteristic of the registration of the color imaging equipment in FIG. 1 and FIG. 2. As illustrated in FIG. 3, the registration of the amount of image deflection Gch-Rch is within 0.2 TV line in the working temperature range, and it satisfies the requirement. However, the registration of the amount of image deflection Gch-Bch exceeds 0.2 TV line, and it does not meet the requirement.